Semiconductor components of the aforementioned type generally have a pn junction between two semiconductor regions that are doped complementarily with respect to one another. In this case, a depletion zone having only a few free charge carriers is formed in the region of the pn junction. The depletion zone is also referred to as a depletion layer or as a space charge zone. The space charge zone is reduced in size or enlarged depending on whether the junction is operated in the forward or reverse direction.
An electric field forms in the space charge zone, the strength of the electric field being dependent on the voltage applied to the junction. Particularly in the case of a junction operated in the reverse direction and a high reverse voltage applied to the junction, the electric field of the space charge zone can reach very high values, which may lead to voltage breakdowns in the semiconductor component.
The profile of the electric field results from the gradient of its electrical potential and is therefore often represented on the basis of equipotential lines, that is to say lines which connect points of equal (electrical) potential.
If the electrical conditions established in an electrical component in a specific state are represented on the basis of such equipotential lines, then the regions at increased risk of voltage breakdowns are found where the equipotential lines become greatly compressed.
Such regions at increased risk of voltage breakdowns occurring typically arise at inhomogeneities of the component such as, for example, at surfaces or interfaces, and there in particular at locations with corners, edges or high degrees of curvature. These also include, in particular, semiconductor junctions as are produced e.g., during the fabrication of doped regions.
The risk of breakdown voltages occurring which destroy or at least damage the semiconductor component is particularly high in the edge region, in particular, of the semiconductor component.
In order to avoid such problems, various solution approaches have been developed for planar structures in order to reduce the electric field as uniformly as possible within the edge region. Therefore, a corresponding arrangement is also referred to as an “edge termination” or an “edge structure”.
One of these solution approaches provides so-called “field rings”. These are at least one doped zone of the semiconductor body of a semiconductor component which is arranged in the edge region thereof and which annularly surrounds the “main or load junction”. However, since the principle of a field ring arrangement is not restricted to an annular configuration of the field rings, the latter are referred to hereinafter as “field zones” in generalizing fashion.
Typical exemplary embodiments of such field zone arrangements are illustrated for example in B. Jayant Baliga: “Power Semiconductor Devices”, published by PWS Publishing Company, Boston 1996, pages 82-99.
The compression of the equipotential lines as mentioned in the introduction and accompanying this the risk of a voltage breakdown in the semiconductor, which exists primarily in the off state of the semiconductor component, is reduced on account of additional charges being provided in the region of the field zones.
FIG. 1 illustrates a typical field zone arrangement in accordance with the prior art using the example of a diode. A section of the diode is illustrated in cross section. The diode has a semiconductor body 1 having an inner region 40 and an edge region 41 adjacent to the inner region 40 in the lateral direction.
The semiconductor body 1 comprises a first, p-doped semiconductor zone 12, which is arranged in the inner region 40 and forms the p-doped emitter of the diode, and also a number of second semiconductor zones 13 that are arranged in the edge region 41 and are spaced apart from one another and from the first semiconductor zone 12 in the lateral direction. The semiconductor zones 13 represent field rings or field zones of the diode.
A pn junction is formed between a third semiconductor zone 11, which represents the n-doped base of the diode, and the first semiconductor zone 12, said pn junction forming a load junction of the diode.
For production engineering reasons, the first semiconductor zone 12 and also the second semiconductor zones 13 have been fabricated jointly during the same method steps, that is to say the application of a patterned doping mask and the introduction of doping particles into the semiconductor body using the doping mask, and therefore extend into the semiconductor body 1 to the same depth proceeding from a first side of the semiconductor body 1 in the vertical direction thereof, that is to say that the dimension d12 of the first semiconductor zone 12 in the vertical direction of the semiconductor body 1 and the dimension d13 of the second semiconductor zones 13 in the vertical direction of the semiconductor body 1 are identical.
This fabrication method has the disadvantage that the dimension d13 and the region of extent of the field zones 13 in the vertical direction of the semiconductor body 1 are prescribed by the dimension d12 of the first semiconductor zone 12 in the vertical direction of the semiconductor body 1.